The present invention relates to a new water absorbent matter and a method for producing this matter. In detail, this invention relates to a new water absorbent matter, which is consisting of a mixture of a cellulose fiber and a water-absorbent resin particle and which is stable physically and chemically even after absorbing a liquid, and it relates to a method for producing this matter.
The present invention relates to a method for producing a new type water absorbent. In detail, the invention relates to a method for producing a water absorbent which shows superior water-absorbent properties by a sole use of the water absorbent and displays a very superior water-absorbent effect in a case of being converted into a complex with a cellulose fiber.
The present invention relates to a new water absorbent, an absorbent matter containing this absorbent, and a method for producing these. In detail, the present invention relates to a new water absorbent having a superior water-absorbent property in its sole use and also, displaying a very superior effect in a case where it makes a complex with a cellulose fiber, as well as it relates to an absorbent matter containing the water absorbent and a method for producing this absorbent and matter.
In recent years, water-absorbent resins which are able to absorb water in a range of from several ten times of their own weight to several hundred times have been developed, and, various kinds of the water-absorbent resins have been used for usage which needs water-absorption and water-holding, that is in the fields of sanitary materials such as goods for menstrual periods and disposable diapers, etc., of agriculture and gardening, of foods such as freshness maintenance, etc., and of industries such as materials for preventing dew-forming and for maintaining refrigeration, etc. As the water-absorbent resin there have been already known crosslinked polyacrylates and crosslinked starch-polyacrylate graft polymers.
Since the water-absorbent resin is generally powder, its sole use is few and it is used as a water absorbent matter such as a diaper etc. by mixing it with a hydrophilic fiber such as pulverized pulp, paper, or the like (for example, refer to U.S. Pat. No. 3,888,257 and others). In an use which requires to absorb a lot of water in a short period of time, a sole use of the water-absorbent resin is not enough to absorb the water in a short period of time and, thus, to prevent water-spreading, mixing of the above kind is particularly necessary. The cellulose fiber has a function of holding a powder type water-absorbent resin and, since the water-absorbent resin takes time to absorb water, a function of holding water around water-absorbent resin particles until the time necessary for absorption, and a function of spreading water to the water-absorbent resin particles distributed by a capillary tube phenomenon.
There have so far been offered a quite number of proposals for the method for elevating a water-absorbing velocity and a water absorption amount under pressure. For example, in Japanese Official Patent Gazette, showa 63-19215, there has been disclosed a method which comprises mixing a water-absorbent resin powder having a carboxyl group with a polyvalent amine compound and, if necessary, thermally treating to crosslink a molecular chain adjacent to the surface. In Japanese Official Patent Gazette, heisei 1-17411, there has been disclosed a method which comprises mixing a water-absorbent resin powder having a carboxyl group with a polyvalent alcohol and a compound of one kind or two or more kinds selected from a group consisting of water and a hydrophilic organic solvent in proportions of from about 0.001 to 10 parts by weight of the polyvalent alcohol and from about 0.01 to 8 parts by weight of the compound against 100 parts by weight of the water-absorbent resin powder, heating the mixture at a temperature of more than 90.degree. C. to carry out a reaction of the water-absorbent powder with the polyvalent alcohol, and crosslinking a molecular chain adjacent to a surface of the water-absorbent resin powder. In Japanese Official Patent Provisional Publication, showa 57-44627, there has been disclosed a method which comprises dispersing a water-absorbent resin containing an acrylic acid alkali salt as a component constituting a polymer, adding a crosslinking agent having two or more of a functional group capable of reacting with a carboxyl group (for example, ethyleneglycohol diglycidyl ether), and carrying out the crosslinking. In Japanese Official Patent Provisional Publication, showa 60-163956, there has been disclosed a method which comprises, in the presence of a water-absorbent resin which contains a monomer unit having a carboxylate as a component constituting a polymer and an inert inorganic powder (water-containing silicon dioxide, etc.), absorbing a crosslinking agent (a diglycidyl ether-based compound, a polyvalent metal salt, a haloepoxy-based compound, an aldehyde-based compound, and an isocyanate-based compound, etc.) and water and then, heating with stirring to carry out a crosslinking reaction and water-distillation. In Japanese Official Patent Provisional Publication, showa 60-36516, there has been disclosed a method which comprises immersing followed by polymerizing a hydrophilic monomer having a functional group reactive for a highly water-absorbent resin having a carboxyl group, of which water content is adjusted at 50% by weight or less [a nitrogen-containing vinyl monomer such as (meth)acrylamide and N,N-dimethylaminoethyl methacrylate; a oxygen-containing vinyl monomer such as 2-hydroxyethyl methacrylate; a sulfonate-containing vinyl monomer such as vinyl sulfonate; and a nitrile group-containing vinyl monomer such as acrylonitrile, etc.]. In Japanese Official Patent Provisional Publication, 60-255814, there has been disclosed a method which comprises adding by spraying a crosslinking agent (diglycidyl ether-based compound, a polyvalent metal salt, and a haloepoxy-based compound) under a condition of stirring a water-absorbent resin containing a monomer unit having a carboxylate group as a component constituting a polymer and an inert inorganic powder, then heating to carry out a crosslinking reaction, and then distilling-off water. In Japanese Official Patent Provisional Publication, heisei 2-248404, there has been disclosed a method which comprises crosslinking a water-insoluble, highly water-absorbent resin having a COOM group (M is a hydrogen atom or an alkali metal atom) in a side chain by a reaction product from epihalohydrine and ammonia or an amine. However, the water absorbent matter obtained from the abovementioned arts known in public, for example, in a case where it is used as a water absorbent matter for disposable diapers, because a binding force among cellulose fibers is weaker when a proportion of the water-absorbent resin particles becomes higher, there takes place in an actual use the moving and falling-off of a water-absorbent resin swelled after urine-absorbing and, thereby, there has been found a problem that the water-absorbent performance does not appear as in an expected degree or a problem that the performance does not appear as projected, because the water-absorbent resin particles decomposes by an ingredient in urine.
Also, a water-absorbent resin improved by the abovementioned arts known in public shows in some degree elevation in the water-absorbent property of the water-absorbent resin itself, but in the case where the resin was mixed to make a complex with a cellulose fiber, the water-absorbent property was unsatisfactory. Especially, when a proportion of the water-absorbent resin becomes higher, a binding force among cellulose fibers becomes weaker, so that there easily occurs the falling-off of the water-absorbent resin. This defect has been known in some examples at the present stage; for example, in a case where the water-absorbent resin is used as a part of a water-absorbent matter in a disposable diaper, the water-absorbent resin swelled after urine-absorption shifts or falls off due to movement of a wearing body, thereby the water-absorbent performance is not displayed in such an extent as expected. Such a phenomenon as the shifting and falling off of the water-absorbent resin is a great handicap in various use of the water-absorbent resin. In practical use, although it may be said that an ideal water-absorbent resin is such as capable of sufficiently deriving an effect mutually potentiating (a synergistic effect) with a complex-making partner material such as a cellulose fiber etc., such one as well as a water absorbent matter not showing the moving and falling-off of a water absorbent resin after absorbing water are not yet obtained at the present stage.